The present invention relates to a bus transmission system, and more specifically to a bus transmission system for transmitting data at high speeds between a computer and input-output devices.
In the conventional widely employed bus transmission system, two or more transmitter-receivers are connected to a single transmission line, the individual transmitter-receivers being connected to a drive circuit and/or to a receiver circuit such that information can be transmitted between them in both directions or in one direction only. In the above-mentioned system, the number of the transmitter-receivers connected to the same line varies depending upon the scale of the system. When the data is to be transferred at high speeds using the above transmission system, both ends of the line are terminated in a matched manner, and the input impedance of the receiving circuit is increased so as not to affect the transmission of signals.
On the other hand, when the transmission system is not required to transmit the data using the bus between the computer and the input-output devices, the power supply for the transmission system will often be turned off. The power supply for the transmission system will be turned on only when the transmission system is required to transmit data.
The above-mentioned requirements, however, are not satisfied by the conventionally employed circuits. According to the open-emitter drive circuit system which has been proposed thus far to satisfy the above-mentioned requirements, the residual voltage greatly affects the signal waveforms and imposes a limitation on the length of the transmission line or on the speed of data transmission.